There are various types of swimming and diving fins with diverse features and properties for use in pools and in the open water, by athletes, snorkelers, scuba divers, lifeguards, and others. Swimming fins are one type of fin that is used in fitness swimming or in performance training for competitive swimming sports. Such swimming fins can add resistance to a swimmer's kick and thereby provide the strength training that would ultimately allow a swimmer to swim faster and for longer than without the fins.
Swimming fins are primarily designed to increase the surface area of a swimmer's foot in order to add more propulsion force that would allow a swimmer to swim faster. Maintaining a higher speed of swimming generally requires more work and sustained exertion of energy from a swimmer, and thus can help build a swimmer's strength. For example, a swimmer attempting to swim at the same high speed without the fins would tire out faster and be unable to maintain that pace for a long period of time, and thus be unable to build the same amount of muscle as when using the fins. Thus, while swimming fins primarily cause a swimmer to swim faster when in use, they provide secondary benefits in gradual strength training. However, improvements can be made to conventional swimming fins that, for example, are designed with the primary goal of increasing swimming speeds rather than maximizing the resistance load to the swimmer's kick.
Various improvements have been made to swimming fins through the years, depending on their use and purpose. Certain improvements have been inspired by the natural swimming features of aquatic animals or marine mammals. For example, many swimming fins are based on the webbed footing design of animals such as ducks, which increases propulsion force by providing an improved oar-like pushing against the resistance of water and an improved recovery stroke. Other animals use different systems of propulsion based on a more flexible blade and a wing-like type of movement to simulate, for example, a whale's tail (see, e.g., U.S. Pat. Nos. 5,906,525; 5,906,525; 4,541,810) or a dolphin's tail (see, e.g., U.S. Pat. Nos. 2,321,009; 4,055,174). However, the features of small aquatic animals or large marine mammals are not always compatible with the biomechanics of a human swimmer. For example, the swimming fin shaped like a dolphin's tail disclosed in U.S. Pat. No. 4,055,174 achieves good aquatic properties, but by connecting the swimmer's feet together, forces the swimmer to kick in an unnatural and inefficient manner (and further precludes walking with the fins). While the ‘biomimicry’ of certain features in aquatic animals can be useful and may provide certain advantages in propulsion force or fluid dynamics that can improve a swimmer's kick, swimming fins should not so closely simulate the features of animals as to disregard the natural mechanical functions and balance of a human or cause a swimmer's body to be thrown off its ideal swimming position in the water.
Swimming fins are typically of one of two types—the closed foot type or the open heel type with a fastening strap. The closed foot type of fin is generally shaped like a shoe, with a cavity at the base shaped to fit a user's heel, and a foot pocket extending into the fin from the cavity. While the closed foot type has the advantage of providing stability and secure connection to the foot by providing a rigid edge to a user's heel and support to at least a part of the ankle, it does not allow much flexion to the ankle and thus inhibits the full extent of a swimmer's kick and natural swimming motions. The closed foot type of fin also has the disadvantage of being burdensome to manufacture because like regular shoes, it must be formed in various sizes to fit each individual foot size. However, open heel fins do not provide as much stability or security as the closed heel type of fin since they do not sufficiently support a swimmer's heels. In addition, the strap of an open heel fin may add stress to the back of a swimmer's heel, for example in the Achilles tendon area, and cause discomfort to a swimmer.
Thus, there is a need to address these and other problems to improve swimming fins for use as a training accessory for fitness and performance swimming, for the purpose of building the strength that can enable a swimmer to swim faster and for longer periods of time when not using the fins.